Composite structure with triangular shear connectors



Aug. 16, 1949.

WITH TRIANGULAR ECTORS C. P. CUENI COMPOSITE STRUCTURE SHEAR CONN FiledMarch 16,

4 rra/e/viy Patented Aug. 16, 1949 E9 "OFFICE --QOMOSITE STRUCTURE WITH'TRI- ZNGULAR SHEAR CONNECTORS 5 Claims. ,1! V

This invention "is di'rectedtto eomposae structures consisting'es'sieh'tieillyofsteel'nr other beams and a reinforcedconcreteslabsupported by the same and united=thereto by-zthe usemfsshearireinforcements extending 11mm :said-ibeam rintorsaid concrete.

More particularly, the present invention is directed to shearcommentsanchor the slab to the beams$andthi1siproviding a unitarfistructurewhich characterized by lightness =and rgreat strength.

.It .has been rcustomary-ior'ra number of years to pfovide'stru'turesof'this kind wherein .the upper flanges of thesteelbeams were providedwith shear" connectors; consisting of *s'teel bars bent :into;=helical:shape -;and iwiel'ded tn-Title .t'op flange f the .steel -:,beams,aas-ris- :des'cribed ain the patent to Schaub No. 2,016,616. .Such aconstruction has numerouyadvantag'es, and is used extensivelyoHoweveriibecauser'of theurse ctsinuous rods, it sometimes becomesdiflicult to insert, in their proper :positions; theesteelzreinforcementfor the concrete slab. -Anothertdisadvantagecf the bent r'o'dconnectors-is:their vulnerability. If they are welded inzthe sshopltothe top flange of the steel beams, the connectors .may the damaged 'ordeformeii susm rsmtpm or"erection. Also, the connectorsmn {top or beamsmay interfere with Walking th'e beams diirinxgoei'ection or makedifiicultrtheierectien of a, working platform on top of the erectedbeams. For -this reason, "the" bar "connectors; are usually wldedin thefield-after -"the beamsai e gei'ect'e'd. 'JIl'iis is much moreexpehsiveandthefild welding is'enot asreliahleas theshopwelhhtg.

Therehave' also-been 'u's''d. shear "connectorsifor steelbeamswhereiri'a; number of spaced elements consisting'of anangleisectionwere-welded to the top flange ofthe beam withrone ofthe Iaces lyin fiaton-saidflange. This-construction.allowedrthe placing of "t'hereinforcemeiits "for'jthe concrete slabs, but had the disadvantage thatthere was no great resistance to a certain" bendin lmoment set up by thehorizontal shearonthe erectLmember ofitheanfgle. (The -erect memberlhas.therer foreto be designed on"bending Whichmakes such a connectorprohibitive. "The same is true of aa plate connector, consisting of .a'square or .reotangular plate Standing'on-cneedge and-welded to the beam.

There'have also been used shear connectors consisting ofstrn'ctui'alshapes standing upright on the 'top'fiange of the steel beams, andwelded thereto insuchha .wayrthat they wereestifi ienoughto'tran'sniit'the shear forcesrwithoutrbendins."and

also effectivel prevented the fslab. from rlifting upwardlylfrom thebeam, :as described in my Patent No. -2',-340,l-7.6. Theseconnectors'take more space, longitudinally .oi the tbeam, than-.aneangleor. a. platimrectanahlanplate :stand-ing omits edge,

and therefore .may interfere with the placing or 'theislabreinforcement. In structures .withheavy unit"horizorital shear thesestifficonnectors may be so .close together that the placing or thebottom slab reinforcin becomes difficult. Furthermore, in suchstructuresthe small 'spacebetween thecbnntitom makesit difficult to transmittheshear stresses into the concrete. This transmisstem of "thesh'ean'stresses into the concrete-is effiected by the compression of theconnector agairist' the concrete. If the space between two connectors issmall the shear value 'of' the concreteravill'ibe the governing 'factorand not the compression value. If the shearstr-ength "of the concrete,which 12s much *smaller'than its compressive strength, :is exceeded,athe concrete 'pro tnuding between two connectors will be zshea'rfed off:hef ore ithe allowable compressive strength :of therconcrete isreached.

lfhis disadvantage applies even a more to-angle and plate connectors,rand. -.ehannel and a bar connectors "standing with one .flange'on topof thebeam.

illhe presentinvention is intended and adapted to overcome thedisadvantages of prior. structures andrpro'vide shear connectorssecuredto the steel erntherTbeams which will haveadequatestiffness,yer'wm provide. sufficient space between two adjacentconnectorsto'transmit the stresses into the concrete.

Accordingly, it is among the objects of the present invention to providea compositestructure'wherein *the-beam has shear reinforcementsproviding "an adequate resistance against shear and, titthe-s'ame time,provide "for'the use of reinforcements in the lower part of the concreteslab.

It is also among the objects of the'present invenom-to provide acomposite structure in which the shear eonnectors are of such form andar rangement as to give' the maximum resistance *to shear 'whiler'at thesame time, utilizing a minimumwightotmeta'l.

-fin1practicingthe present invention, the same i-s based upon thefactthatwith'-a1l shear connectors that itransmit =.the stresses "into theconcrete bycompression the "stresses -acting *on the compressionia'ce'cfithe connector form a' diagram of parabolic shapawhich is 'wellapproached by :a'itria'ngle, theistressat the top'being'zero and at thebottom, near the top fiber o'f' the steel hearmreaching-the maximum.

l he*point rif attack of the resultant of ail stresses '-is '.thereforeone-third up from the'base of itheilconnector. The lever arm for thecomplitation-rof ithe bendingamoment prcduceii by the horizontal shearfor any"connector =with a compression ifa'ceflo'f rectangular shape isthere- Iore onesthirdroftheflepth "of the connector. A'c- A cording stothe present-inventiong by using a-plate shear connector Of roughlytriangular shape, most of the less eilective top part of the plate iselimi hated and the lever arm for the computation of the bending momentis reduced from one-third to one-fourth of the depth of the connector,that is, the height upwardly from the' beam. These two seemingly smalldifferences make a triangu-- lar connector much more economical than arectangular one and provide more space for the introduction of thecompressive stresses into the concrete.

To prevent uplift of the concrete slab, the connectors may he providedwith a hook at the upper corner, or may be inclined toward the center ofthe beam. 7

In the accompanying drawing constituting a part hereof, and in whichlike reference characters indicate like parts:

Figure 1 is a transverse vertical cross-sectional view of the steelsection and shear connectors of a composite section, some parts beingbroken away for clearness;

Figure 2 is a longitudinal cross-sectional view of the structure ofFigure 1, part of the concrete slab being broken away to show theconnectors;

Figure 3 is a perspective view of a beam with shear connectors thereonprior to the pouring of the concrete slab; and

Figure 4 is a view similar to Figure 3, but showing different forms ofconnectors.

The structure according to the present invention consists generally of asteel or other beam I, only partly shown in Figure 1, with a. top flange2, shear connectors 3 and 4 and a concrete slab 5. As shown in Figure 1,the shear connectors 3 and 4 consist of plates of triangular shape whichare welded to the top flange 2 of the steel beam, and are well embeddedin concrete slab 5. Top reinforcing bars 6 and bottom reinforcing bars Iof the concrete slab are also shown. Shear connectors 3 and 4 may be ofthe same shape and dimensions, but are placed alternately on oppositesides of the flange. The spacing may increase toward the center of thebeam according to the actual stress.

In Figure 2 the top flange 2 to which the shear connectors 3 and 4 areattached by welds 8, supports concrete slab 5. The connectors are weldedto the flange in inclined positions, providing resistance againststresses tending to lift the slab from the beam.

With the shear connector 3 in Figure 2 is shown stress diagram 9 withthe arrows 10 indicating the direction and magnitude of the stresses..Because the stress diagram is of triangular form from both sides, inother words, forms a pyramid the point of attack of the resultant II ofall stresses is at one-fourth of the depth of the connector from thebase. fc shows the maximum concrete stress. An example will illustratewhat advantage a triangular connector has as compared with heretoforeused connectors. Assuming the unit horizontal shear per lineal inch is2,500 pounds, the thickness of the concrete slab 7 /2" and the requiredheight of the connector is 4%". This does not mean that the wholeconnector has to reach 4%" up into the slab, part of it is sufiicient.The allowable stress for the concrete is assumed to be fc: 1,000 p. s.i., and for the steel fs=20,000 p. s. i.

The allowable load per shear connector has to be computed with respectto concrete and steel stresses, the lower one governing the design.

1. Design of triangular plate Assumptions: plate of'%" thickness,'6"base and 4%" height.

a. Allowable load for one connector with respect to concrete stress:

F=fcX 6 X 4.75/3=9.5 fe=9,500 2) b. Allowable load with respect to steelstress: The section modulus of the plate at the base Ss=6 X 0.75 =0.5625in.

The bending moment produced by the resultant of the shear stresses:

M=fc 6X4.75/3 4.'75/4=11.28 fa fs=20,000=M/Ss=fe 11.28/0.5625=20 fcfc=20,000/20=1,000 p. s. i. F=9.5 1,000=9,500 112 Both a and 12 give thesame value. Spacing required=9,500/2,500:3.8 in. Weight of connectorsper ft. of beam:

2. Design of rectangular plate Assumption: plate of thickness, 6" baseand 4%" height.

a. Allowable load with respect to concrete stress:

:fcX 6 X 4.75/2=14.25 is: 14,250 17 b. Allowable load with respect tosteel stress: The section modulus is the same as under 111.

Ss=0.5625 in.

The bending moment produced by the shear stresses:.

Therefore the steel stress governs, and the spacingrequired:7,125/2,500=2.85 in.

Weight of connector per ft. of beam:

The triangular plate connector saves 62% in weight as compared with therectangular plate connector. Besides the rectangular plate connectorsare spaced only 2.85" apart which is by far not enough to transmit thestresses safely into the concrete. No doubt the concrete protruding intothe space between two plates would shear ofi. With the triangular platesthe spacing is 3.8" which still would not be enough for rectangularplates, but it is sufiicient for a triangular plate because if placed asshown in Figure l, the spacing for most of the compressive area is2x3.8=7.6 in.

The triangular plate connector has another advantage. A timber, such asa 4" x 4" or 3" x 3", can easily be placed on top of the connector inthe center, along the beam, and will be held well in place by the twoinclined edges of the shear connectors. A working platform can easily bebuilt on top and nailed to these longitudinal wood supports. Theseconnectors do not at all interiere with the placing of the slabreinforcement, as is well shown by Figs. 1 and 2. They are also muchless vulnerable to damage than, for instance, a spiral connector.

Figure 3 shows triangular shear connectors l2, I3 and I 4 weldedperpendicularly to the top flange 2 of beam I. Connectors I2 and I4 arewelded on one side of thebeam and on the other side, in the centerbetween them, is welded connector l3. This arragnement doubles theshearing area of the concrete and makes for better lateral distributionof the compressive stresses in the concrete.

Because the direction of the horizontal shear near the supports is at anangle to the horizontal, the shear has a vertical component and theconnectors must be able to take care of it. With triangular connectorsthis can be done by welding a horizontal bar I5 to connector IS, or byplacing the connector at an acute angle to the top flange 2, as shown byconnectors I1 and I8 and in Figure 2. For the same purpose the top ofthe triangular connector can be bent to form a hook, as shown byconnector l5. Instead of straight bar l5 a hooked bar may be welded tothe connector.

Figure 4 shows I-beam l which may be a rolled section with or without acover plate or a builtup section, and having a top flange 2. Shearconnector 29 has the shape of a channel with flanges 2| and 22, and totake advantage of the section modulus of the web and both flanges, thetriangular section is modified to become a trapezoid. This reduces inpart the advantages of the purely triangular section, but makes thechannel still more economical than any other way. The channel could alsobe used with the flange 2| sitting on top of the beam flange 2 andflange 22 would reach into the concrete and form an anchor to resistuplift forces. However, this would be a more expensive channel connectorthan the one shown in Figures 1 to 3.

Connector 23 is in the shape of a pyramid, and, therefore, itscross-section is better adjusted to the bending moment than a connectorof triangular shape. Compared with connectors 3 and 4 or I2 to hi it hasone-third less weight, but cannot be cut from standard rolled sections.

24 and 25 show connectors cut in triangular shape from T sections. Thetriangular shape of a T connector is more economical if the T connectoris governed by the steel stresses, and not the concrete stresses. Theupper part of connector 25 is bent to provide effective anchorage in theconcrete slab.

If the unit shear is not very high or connectors are used that have agreat section modulus, the spacing will be increased enough to place theconnectors in the center of the beams, as shown by connector 20. If thewidth of the connectors is small two may be placed at the same level, asshown by connectors 24 and 25.

Although the invention has been described by several specific examplesof various connectors, the invention is not limited thereto, since anyshear connector, the design of which is governed by the bending momentproduced by the shear stresses will profit by a triangular shape. Otherforms than those specifically described may be used, as, for instance,the shape of the triangles may be different from those shown, as, forexample, they may be equilateral, scalene, or other forms. Theconnectors need not be true triangles, but the benefits of the presentinvention are obtained when connectors are approximately or roughlytriangular, as, for example, the sides need not be straight, but theremay be some curvature therein either concave, convex or combinations.

In the claims the term beam" is intended to include not only thestandard commercial shapes, but any built up welded or riveted beamsection, as well as trussed joists that may be rolled or welded. and theterm triangular is intended to include an approximately triangular formand also shapes wherein the edges are other than straight lines.

What I claim is:

1. A composite structure comprising a beam having a top flange, saidflange having an unbroken suriace and having parallel side edges, aplurality of shear connectors of triangular form, one edge of eachconnector resting on said flange and extending from the side edge ofsaid flange to at least the center-line of said beam at right angles tosaid side edges, said connectors being adjacent both of said side edgesand being welded to said flange.

2. A composite structure comprising a beam having a top flange, saidflange having an unbroken surface and having parallel side edges, aplurality of shear connectors of triangular form, one edge of eachconnector resting on said flange and extending from the side edge ofsaid flange to at least the center-line of said beam at right angles tosaid side edges, said connectors being adjacent both of said side edgesand being welded to said flange, the face of said connectors beinginclined to the surface of said flange.

3. A composite structure comprising a beam having a top flange, saidflange having an unbroken surface and having parallel side edges, aplurality of shear connectors of triangular form, one edge of eachconnector resting on said flange and extending from the side edge ofsaid flange to at least the center-line of said beam at right angles tosaid side edges, said connectors being adjacent both of said side edgesand being welded to said flange, an extension on said connectors atright angles to the face thereof fixed on said flange.

4. A composite structure comprising a beam having a top flange, saidflange having an unbroken surface and having parallel side edges, aplurality of shear connectors of triangular form, one edge of eachconnector resting on said flange and extending from the side edge ofsaid flange to at least the center-line of said beam at right angles tosaid side edges, said connectors being adjacentboth of said side edgesand being welded to said flange, pairs of said connectors being inalinement transversely of said flange and in substantial contact witheach other.

5. A composite structure comprising a beam having a top flange, saidflange having an unbroken surface and having parallel side edges, aplurality of shear connectors of triangular form, one edge of eachconnector resting on said flange and extending from the side edge ofsaid flange to at least the center-line of said beam at right angles tosaid side edges, said connectors I being adjacent both of said sideedges and being welded to said flange, the highest point of saidconnectors being above said side edge, said connectors sloping from saidpoint to said surface.

. CLEMENT P. CUENI.

REFERENCES CITED The following references are of record in the flle ofthis patent:

UNITED STATES PATENTS Cueni et al Jan. 25, 1944

